i'm a former marine. military training doesn't involve weight lifting, and i was upset about that. in boot camp, it's not just the regular training that conditiones you, it's EVERYTHING. take the M-16....a 7.2lb rifle..it's nothing, right? heh heh, think again! imagine holding it by the front grip, rifle is straight up and down, your arm is straight out from your body...oh, yeah, that's with ONE hand. keep it there for, hmmm, 2, 3, 4 minutes. easy? i wish! force yourself to do 20 pullups...whether you can do them or not. can't make 20? ok, well, you're not done. someone will come and grab your feet. you'll bend your knees so your feet are up behind you, and you'll get an assist to get you to 20. thankfully i was able to do 12 or 13 when i went into boot camp...i feel bad for the guys that could only do 5 or 6. at the end of bootcamp my personal best was only 16 or 17...takes a LOT to get 20. and these pullups are pure deadhangs too. overhand or underhand, unless you're told specifically which way to do them.
try 6" for a few minutes. jumping jacks for 5+ minutes. or here, try this....
on command, go from running in place (knees coming up to waist height), jumping jacks, flutter kicks (6" while alternating which leg you are lifting, and yes, the other leg stays up), pushups, mountain climbers (on hands and feet, kinda in a running in place motion)...all sorts of stuff. now, continue to do it for 10, 15, 20 minutes...maybe longer. you could be stuck in one exercise for a few minutes or changing exercises every 15 seconds. do all this AS FAST AS POSSIBLE. one day i did all this for almost an hour and a half, with one 5 minute break. know what i did to deserve that? i farted.
so besides the regularily scheduled training days, you can be nailed with extreme cardio at any time. they build time into the schedule for these things, so i guess it's scheduled training.
so with enough use of your own bodyweight, you can gain strength, and even size, as everyone told me my back and shoulders grew a lot while i was in boot camp. military training is for strength though, as they want you to be lean and mean killing machines.